The present invention relates to a rotary pump for liquid and more particularly to a rotary pump of the immersed rotor type with a bearing wear indicator.
The present invention is particularly applicable to a liquid rotary pump where the liquid immerses the motor rotor that is isolated from the motor stator by a seal often referred to as a can or jacket. This type of speciality pump has been manufactured for many years and includes a shaft for rotatably mounting the rotor of the motor element of the pump. To center the rotor in the pump housing, it has proven quite beneficial to use a mechanism having axially spaced conical bearings. Such pump and bearings are disclosed in Young U.S. Pat. No. 3,195,466. Conical shaft bearings not only center the rotor and maintain the axial position of the pump impeller, but also provides the friction bearing surfaces between the pump housing and rotating elements within the pump. Young U.S. Pat. No. 3,195,466 is incorporated by reference as background information so that the details of the particular pump and bearings to which the present invention is directed need not be repeated by merely describing known pump technology. Through the years, patents have issued directed toward certain mechanical changes in an immersed rotor type of liquid pump. Two of these patents are Spisiak U.S. Pat. No. 3,225,698 and Neal U.S. Pat. No. 3,433,164. These patents are also incorporated by reference herein as background pump technology that need not be repeated in describing and understanding of the present invention. Recently, anew design for an immersed rotor rotary pump was the subject of Brunet U.S. Pat. No. 6,350,109. This patent replaces the conical bearings with a combination of radial and thrust or axial magnetic bearings whereby the immersed rotor essentially levitates as it rotates. This is a drastic departure from the simple conical bearing construction used over the years and requires substantial electromagnetic controls to maintain the levitation gaps. However, this patent does teach a pump of the type to which the present invention is directed and is incorporated by reference herein as background information and for again showing pump components not involved in the present invention. The rotary pump to which the present invention is directed is an improvement or modification of an existing pump sold by Buffalo Pumps of North Tonawanda, N.Y. The interior design of the preferred embodiment is the same as the pumps marketed by Buffalo Pumps for some years. This well known design is disclosed in Bulletins 929A and 985 which are incorporated by reference herein as background information that shows how the pump to which the present invention is directed complies with the background technology of the patents heretofore incorporated by reference. These bulletins also disclose the fluid thrust balancing mechanism used in some of the immersed rotor pumps, but this feature does not constitute a part of the present invention. All this material is disclosed to show the concept of a pump to which the present invention is directed and use of axially spaced conical bearings for supporting the immersed rotor of such pump.
The immersed rotor type of rotary pump which has proven to be the most successful through the years includes axially spaced conical bearings. The conical bearings have a journal element that is self lubricating carbon graphite with an internal taper and mounted for axial movement in the pump housing. The internal taper or conical bearing surface of the journal matches the taper or conical bearing surface of an element supported on the shaft of the immersed motor rotor. In this type of pump, stainless steel coil springs in the journal recess of the pump housing force the axially movable bearing elements or journals toward the fixed, matching elements on the rotor shaft. Thus, from both ends of the rotor a coil spring biases the two journal elements of the spaced conical bearings into engagement with the shaft elements to provide a bearing force that maintains the radial position of the rotating rotor. In addition, the conical bearings have a force component that maintains the axial position of the rotor within the pump housing. Consequently, the conical bearings which have been used for decades are quite successful and constitutes an inexpensive mechanism to maintain self-centering of the rotor for control of both the radial and axial positions of the rotating components of the rotary pump. During normal bearing wear, the conical bearings maintain the radial position of the rotating components of the pump. In addition, one of the beneficial features of using conical bearings is that the bearings have a self-centering ability in a axial direction based upon the liquid pressure around the rotor. The thrust balancing feature uses the pressure differential between the front of the rotor and the back of the rotor so that the hydraulic forces move the conical bearings slightly to center the rotor. This balancing is accommodated by spring biased conical bearings.
The conical bearings that are spring biased have an initial axial position after thrust balance, which position should be maintained over long term use of the pump. When the conical bearings have reached approximately xe2x85x9 inch of wear, it is desirable to replace or repair the journals of the pump to maintain trouble free operation. Wear of the conical bearings is normally discovered during regular inspection involving disassembly of the pump. However, it is desirable to know the extent of bearing wear for the purpose of tending to proper preventive maintenance. At this time, rotary pumps of the immersed rotor type are subject to periodic maintenance or inspection. The time between such inspections must be quite short to assure that maintenance is performed before the pump fails due to bearing wear. Catastrophic bearing failure must be avoided. Bearing wear can be accelerated by the type of liquid being pumped or contaminants. Consequently, it is preferred practice to inspect the conical bearings long before they need to be refurbished to assure long term operation of the pump. These factors make maintenance of the conical bearings a relatively costly and time consuming activity.
The present invention relates to the concept of monitoring wear of the conical bearings to determine when they should be replaced and/or refurbished. Consequently, frequent inspection of the bearings is not necessary. Bearings are given attention only when actually needed. This is a substantial advantage, is cost effective and prevents catastrophic failure based upon bearing malfunction. In the past, such failure could occur between even short term inspections. The invention involves an improvement in a rotary pump of the type described and incorporated by reference herein. Real time monitoring of conical bearing wear is the result of using the invention. A wear monitoring device using a magnetic mechanism is associated with each of the axially spaced conical bearings. A simple base line position is set during initial installation or start-up of the rotary pump. This base line compensates for assembly tolerances associated with bearing spacing. After initial set-up, the monitoring device is periodically inspected to reveal when the conical bearings need to be inspected or replaced. The magnetic device is installed on the motor housing at a position dictated by the location of the conical bearings. A magnet is implanted in each spring biased, axially movable journal of the pair of conical bearings. During operation of the pump, the conical bearings and the rotor assembly move axially to maintain the hydraulic thrust balance as previously described. In this instance, the magnets on the bearings move in the same direction and retain a balanced condition. As the conical bearings wear, the magnets in the bearing journals move toward each other as the journals move toward each other. The actual positions of the journal magnets are monitored by using the present invention. When there is a given distance of inward movement, in practice, xe2x85x9 inch, a visual indication is outputted for the purpose of inspection and replacement of the worn bearings. Thus, the present invention gives an indication of when bearing wear is a given amount. This change in spacing of the bearing journals is indicative of the need to replace the bearings or otherwise attend to the bearings in the pump. The wear monitoring device of the present invention allows axial movement of the conical bearings in unison in a given direction while being able to detect wear as the journals move in opposite directions. The device is easily installed on existing canned pump designs. There is no need to modify the pump pressure boundary or to disturb the integrity of zero leakage design. By merely assembling a wear detector element in the housing of the pump adjacent each of the conical bearings, the wear characteristics of the bearings is monitored by using the present invention.
The invention is used in combination with a rotary pump of the type including a housing, an impeller rotatably mounted in the housing by a shaft carrying a motor rotor, and a motor stator fixed in the housing and surrounding the rotor to rotate the rotor and shaft about an axis. The shaft is mounted in the housing by axially spaced conical bearings, each of which includes a first element fixed on the shaft with a first conical bearing surface concentric with the axis of the shaft and a second element or journal carried by the housing, with the second conical bearing surface of the journal concentric also with the axis of the shaft. The two conical bearing surfaces engage each other to center the shaft for rotation in the stator. Biasing elements in the form of coil springs in the housing recess carrying the journals force the journals toward each other in an axial direction to compensate the wear between the surfaces. The journals are cylindrical in cross section and reciprocate in the recesses or chambers of the pump housing in only the axial direction. In accordance with the invention, a novel wear indicator mechanism is provided for this type of rotary pump. The wear indicator mechanism includes a first permanent magnet in the journal of one bearing and a second permanent magnet on the journal of the second bearing. A first follower mounted on the pump housing has a third permanent magnet facing the first magnet on one of the bearing journals. This follower is movable as the bearing on the journal shifts axially. A second follower is mounted on the pump housing with a fourth permanent magnet facing the second permanent magnet on the second journal and is movable by axial movement of the second permanent magnet on the second journal. Each of the followers has an indicator element movable into a position indicating the moved axial position of the first and second permanent magnets. The monitor device or mechanism measures the position of permanent magnets or the journal to indicate wear of the conical bearings.
In accordance with a further aspect of the invention, each of the magnet followers is a pendulum pivotally mounted about an axis generally perpendicular to the axis of the shaft. The pendulum has a first end carrying the magnet that follows the magnet on the journal and a second end that constitutes an indicator element for the follower. By using a pendulum mechanism, the two pendulums can be interconnected in a manner where shifting of the magnets in the same direction for fluid thrust balance does not improperly register wear However, when wear occurs, the pendulums are moved by the journal magnets in opposite directions. The amount of movement together indicates the extent of the bearing wear. By using the pendulum mechanism of the present invention, the wear indicator mechanism is allowed to compensate for axial movement in the same direction for thrust balancing of the pump. Some pumps do not have such fluid thrust balancing, but the wear indicator is equally applicable for use in such pumps. By using the novel pendulum arrangement, movement of the journals for the conical bearings together for thrust balancing does not indicate wear. An indication of wear only occurs when the bearings on the journals move in opposite directions as is the situation when there is actual bearing wear.
In accordance with another aspect of the present invention, the first and second followers are mounted in a tubular non-magnetic housing having a lower wall between the magnets in the journals and the magnets on the ends of the followers. In such tubular housings, there is provided an upper viewing opening exposing the indicator element of the followers to visually reveal actual movement of the bearing journals.
In accordance with an aspect of the invention, there is provided a detector switch carried by one of the followers, which switch is activated to provide an alarm when the two followers are shifted to a position indicative of the inward axial movement of the bearing journals a given distance requiring bearing maintenance or replacement.
The primary object of the present invention is the provision of a mechanism for monitoring the actual wear of the two axially spaced conical bearings of an immersed rotor type fluid pump.
Another object of the present invention is the provision of a rotary pump including a mechanism as defined above, which mechanism can compensate for fluid thrust balance in pumps having this operating feature.
Yet another object of the present invention is the provision of a pump having a mechanism as defined above, which mechanism includes two spaced pendulums that are pivoted about axes perpendicular to the rotor shaft, with the pendulums being interconnected in a manner that movement of the conical bearing journals in the same direction does not indicate wear, but in the opposite direction indicates bearing wear.
Still a further object of the present invention is the provision of a mechanism, as defined above, which mechanism reads movement of the journals for the axially spaced conical bearings as they move toward each other indicating wear of the bearing journals.
Still a further object of the present invention is the provision of a mechanism, as defined above, which mechanism includes a switch and alarm circuit to create an alarm signal when the mechanism senses a preselected amount of wear between the conical bearings.